• Jeffrey A Kline, Melanie M Hogg, David R Mauerhan, and Steven L Frick.
• Department of Emergency Medicine, Carolinas Medical Center, Charlotte, NC 28232-2861, USA. jkline@carolina.rr.com
• Clin Physiol Funct Imaging. 2008 May 1;28(3):161-8.

BackgroundThe exhaled end-tidal CO2/O2 ratio and the D-dimer concentration are diagnostic markers of pulmonary embolism (PE).ObjectiveTo develop a non-invasive technique to monitor for PE in surgical patients. We examine the change imparted by anaesthesia-surgery on the end-tidal CO2/O2 compared with the D-dimer.MethodsWe enrolled 125 participants undergoing an orthopaedic or oncological operation thought to confer high risk for postoperative PE. We obtained preoperative blood samples in the anaesthesia clinic, and breath samples in the preoperative holding area on the same day of surgery; we repeated blood and breath samples on the postoperative day of discharge. Blood samples were immediately analysed for fibrinogen and D-dimer (Vidas; bioMérieux, Durham, NC, USA) concentrations. Breath samples were obtained from 1 min of spontaneous tidal breaths delivered via mouthpiece while the participant breathed room air. All participants had follow-up at 30 days.ResultsWe enrolled 125 participants and had complete data in 104. No participant developed PE or deep venous thrombosis within 30 days. The mean preoperative D-dimer was 927 +/- 928 ng ml(-1), and the mean postoperative D-dimer was 1879 +/- 1263 ng ml(-1) and the mean relative change was +234 +/- 292%. The mean preoperative end-tidal CO2/O2 was 0.31 +/- 0.05 and the mean postoperative end-tidal CO2/O2 was 0.32 +/- 0.07 and the mean relative change was +1.6 +/- 20%. The increase in D-dimer did not correlate with the increase in fibrinogen (r2 = 0.015).ConclusionsThe stress impact of anaesthesia-surgery causes less change in end-tidal CO2/O2 compared with the D-dimer. Further work will be required to determine if end-tidal CO2/O2 can be used to monitor for postoperative PE.

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